1. Field of the Invention
Embodiments of the present invention generally relate to a flow operated orienter.
2. Description of the Related Art
Conventional directional drilling with a drillstring of jointed pipe is accomplished through use of a Bottom Hole Assembly (BHA) including a bent sub (typically one-half to three degrees), a drilling or mud motor, and directional Measurement While Drilling (MWD) tool in the following fashion. To drill a curved wellbore section, the drillstring is held rotationally fixed at the surface and the drilling motor will drill a curved wellbore in the direction or orientation of the bent sub. This is termed slide drilling because the entire drillstring slides along the wellbore as drilling progresses. The wellbore trajectory is controlled by orienting the BHA in the desired direction by rotating the drillstring the appropriate amount at the surface.
To drill a straight wellbore section, the drillstring is rotated at the surface with the rotary table or top-drive at some nominal rate, typically 60 to 90 rpm. This is termed rotary drilling. In so doing, the tendency of the mud motor to drill in a particular direction, due to the bent sub, is overridden by the superimposed drillstring rotation causing the drilling assembly to effectively drill straight ahead.
When drilling with coiled tubing, neither rotary drilling nor rotational orientation of the BHA can be accomplished without the addition to the BHA of a special rotating device to orient the BHA since coiled tubing cannot be rotated in the wellbore from the surface. One such rotational device, or orienter, operates by rotating in even angular increments, for example 30°, each time the surface pumps are stopped and then re-started. After each pump cycle, the orienter locks into and maintains its rotational position. This ratcheting device allows the directional driller to position the directional assembly closely enough to the desired toolface orientation to allow the wellbore to be drilled in a particular direction.
One drawback to directional drilling with the ratcheting orienter relates to its inability to drill an effective straight wellbore section. As discussed above, in conventional directional drilling, continuous drillstring rotation is used to negate the directional tendency of a bent-housing motor. This produces a very straight trajectory. When drilling with coiled tubing and a ratcheting orienter, continuous rotation is not possible. Thus the driller is forced to orient slightly left of the desired path and drill some distance ahead. Then after stopping to re-orient right of the desired path, the driller drills ahead again. This process is repeated until the “straight” section is completed. The resulting left-right-left or “wig-wag” wellbore trajectory roughly approximates the desired straight path.
For illustration and a more detailed discussion of rotary and sliding drilling, see U.S. Pat. No. 6,571,888, which is herein incorporated by reference in its entirety.